Download Minerals - CSUN.edu

Rocks and
minerals
Doug Fischer
Geog 106 LRS
Minerals: the building
blocks of rocks
Definition of a mineral
• Natural, Inorganic, Solid
• Orderly atomic structure
• Specific chemical composition
Minerals
Physical properties of minerals
•
•
•
•
•
•
Crystal form
Luster
Color
Streak
Hardness
Cleavage
The mineral quartz often
exhibits good crystal form
Pyrite (fool’s gold)
displays metallic luster
Figure 2.10
Mohs scale
of hardness
Figure 2.12
Three examples of perfect
cleavage – fluorite, halite,
and calcite
Minerals
Physical properties of minerals
• Fracture
• Specific gravity
• Other properties
•
•
•
•
Taste
Smell
Elasticity
Malleability
Conchoidal fracture
Figure 2.15
Minerals
Physical properties of minerals
• Other properties
•
•
•
•
Feel
Magnetism
Double Refraction
Reaction to hydrochloric acid
Minerals
 A few dozen minerals are called the rock-forming
minerals
• The eight elements that compose most rock-forming
minerals are oxygen (O), silicon (Si), aluminum (Al), iron
(Fe), calcium (Ca), sodium (Na), potassium (K), and
magnesium (Mg)
• Most abundant atoms in Earth's crust are oxygen (46.6% by
weight) and silicon (27.7% by weight)
Composition of continental
crust
Figure 2.16
The silicate (SiO4)-4 molecule
Figure 2.17
Common
Silicate
Minerals
• note that
complexity
increases down
the chart
Hornblende – a member of
the amphibole group
Potassium feldspar
Plagioclase feldspar
•
Nonsilicate minerals
• Major groups
• Oxides
• Sulfides
• Sulfates
• Carbonates
• “Native” elements
18
Native Copper
Minerals
Mineral groups
• Nonsilicate minerals
• Carbonates
• A major rock-forming group
• Found in the rocks limestone and marble
• Halite and gypsum are found in sedimentary
rocks
• Many have economic value
An underground halite (salt) mine
Mineral Summary
• Inorganic solids, with specific chemical
makeup and internal structure
• Oxygen is most abundant element in
minerals of continental crust – 47%
• Silicon – 28%
• Metalic (aluminum, iron, magnesium,
calcium, sodium, potassium) – 25%
22
Rocks
• Made of mixtures of minerals
• Three classes
– igneous (solidified from magma)
– sedimentary (cemented from debris)
– metamorphic (modified by heat / pressure)
23
2.1
Which of the following best defines a mineral and a
rock?
1. A rock has an orderly, geometrical internal order of
minerals; a mineral is a consolidated aggregate of rocks.
2. A mineral consists of its constituent atoms arranged in a
geometrical structure; in a rock, the atoms are randomly
bonded without any geometric pattern.
3. In a mineral the constituent atoms are bonded in a
regular, internal structure; a rock is a consolidated aggregate
of different minerals.
4. A rock consists of atoms bonded in a regular,
geometrically arrangement; a mineral is a aggregate of
different rock particles.
2.1
Which of the following best defines a mineral and a
rock?
1. A rock has an orderly, geometrical internal order of
minerals; a mineral is a consolidated aggregate of rocks.
2. A mineral consists of its constituent atoms arranged in a
geometrical structure; in a rock, the atoms are randomly
bonded without any geometric pattern.
3. In a mineral the constituent atoms are bonded in a
regular, internal structure; a rock is a consolidated aggregate
of different minerals.
4. A rock consists of atoms bonded in a regular,
geometrically arrangement; a mineral is a aggregate of
different rock particles.
02.01
Which
of following
the following
best
defines
a mineraland
andaa
2.1 02.01
Which
of the
best
defines
a mineral
rock? rock?
A rock the
has constituent
an orderly, repetitive,
geometrical
3. In aA.
mineral
atoms are
bonded ininternal
a regular,
arrangement of minerals; a mineral is a consolidated
internal structure; a rock is a consolidated aggregate of different
aggregate of rocks.
minerals.
B. A mineral consists of its constituent atoms arranged in a
geometrically repetitive structure; in a rock, the atoms are
randomly bonded without any geometric pattern.
C. In a mineral the constituent atoms are bonded in a
regular, repetitive, internal structure; a rock is a consolidated
aggregate of different minerals.
D. A rock consists of atoms bonded in a regular,
geometrically predictable arrangement; a mineral is a
aggregate of different rock particles.
The rock cycle
Igneous rocks
Form as magma cools and crystallizes
• Rocks formed inside Earth are called
plutonic or intrusive rocks
• Rocks formed on the surface
• Formed from lava (a material similar to magma,
but without gas
• Called volcanic or extrusive rocks
Igneous rocks
Crystallization of magma
• Ions are arranged into orderly patterns
• Crystal size is determined by the rate of
cooling
• Slow rate forms large crystals
• Fast rate forms microscopic crystals
• Very fast rate forms glass
Igneous rocks
Classification is based on the rock's
texture and mineral constituents
• Texture
• Size and arrangement of crystals
• Types
• Fine-grained – fast rate of cooling
• Coarse-grained – slow rate of cooling
• Porphyritic (two crystal sizes) – two rates of
cooling
• Glassy – very fast rate of cooling
Course-grained igneous texture
Slow rate of cooling allows large crystals to form/grow
Fine-grained igneous texture
Fast rate of cooling - only small crystals grow before
everything is solid
Obsidian exhibits a glassy texture
Very fast rate of cooling - glass - no regular crystal structure
Porphyritic igneous texture
Mixed rate of cooling - complicated processes, volcanoes
Classification of igneous rocks
Figure 3.7
Figure 3.9
3.2
The texture of an igneous rock
1. is controlled by the composition of magma.
2. determines the color of the rock.
3. is caused by leaching.
4. records the rock’s cooling history.
5. is controlled by the dominant minerals present.
3.2
The texture of an igneous rock
1. is controlled by the composition of magma.
2. determines the color of the rock.
3. is caused by leaching.
4. records the rock’s cooling history.
5. is controlled by the dominant minerals present.
Note: Coarse-grains
occur when the rock
cools slowly and the
minerals can grow large.
When cooled rapidly, a
glassy texture occurs.
Igneous rocks
Naming igneous rocks
• Granitic rocks
• Composed almost entirely of light-colored
silicates - quartz and feldspar
• Also referred to as felsic: feldspar and silica
(quartz)
• High silica content (about 70 percent)
• Common rock is granite
Granite
Igneous rocks
Naming igneous rocks
• Basaltic rocks
• Contain substantial dark silicate minerals and
calcium-rich plagioclase feldspar
• Also referred to as mafic: magnesium and
ferrum (iron)
• Common rock is basalt
Basalt
Igneous rocks
Naming igneous rocks
• Other compositional groups
• Andesitic (or intermediate)
• Ultramafic
Sedimentary rocks
Form from sediment (weathered products)
About 75% of all rock outcrops on the
continents
Used to reconstruct much of Earth's history
• Clues to past environments
• Provide information about sediment transport
• Rocks often contain fossils
Sedimentary rocks
Economic importance
• Coal
• Petroleum and natural gas
• Sources of iron and aluminum
Sedimentary rocks
Classifying sedimentary rocks
• Two groups based on the source of the
material
• Detrital rocks
• Material is solid particles
• Classified by particle size
• Common rocks include
• Shale (most abundant)
• Sandstone
• Conglomerate
Classification of
sedimentary rocks
Figure 3.12
Shale with plant fossils
Figure 3.13 D
Sandstone
Figure 3.13 C
Conglomerate
Figure 3.13 A
Sedimentary rocks
Classifying sedimentary rocks
• Two groups based on the source of the
material
• Chemical rocks
• Derived from material that was once in
solution and precipitates to form sediment
• Directly precipitated as the result of
physical processes, or
• Through life processes (biochemical
origin)
Sedimentary rocks
Classifying sedimentary rocks
• Two groups based on the source of the material
• Chemical rocks
• Common sedimentary rocks
• Limestone – the most abundant chemical rock
• Microcrystalline quartz (precipitated quartz)
known as chert, flint, jasper, or agate
• Evaporites such as rock salt or gypsum
• Coal
Fossiliferous limestone
Rock salt
Sedimentary rocks
Sedimentary rocks are produced
through lithification
• Loose sediments are transformed into solid
rock
• Lithification processes
• Compaction
• Cementation by
• Calcite
• Silica
• Iron Oxide
Sedimentary rocks
Features of sedimentary rocks
• Strata, or beds (most characteristic)
• Bedding planes separate strata
• Fossils
•
•
•
•
•
Traces or remains of prehistoric life
Are the most important inclusions
Help determine past environments
Used as time indicators
Used for matching rocks from different places
3.3
Detrital sedimentary rocks
1. are classified by particle size.
2. contain a variety of minerals.
3. have clay and quartz as chief components.
4. originate as solid particles from weathering.
5. All of the above.
3.3
Detrital sedimentary rocks
1. are classified by particle size.
2. contain a variety of minerals.
3. have clay and quartz as chief components.
4. originate as solid particles from weathering.
5. All of the above.
Definition: Rock formed from the
accumulation of material that
originated and was transported
in the form of solid particles
derived from both mechanical
and chemical weathering.
Metamorphic rocks
"Changed form" rocks
Produced from preexisting
• Igneous rocks
• Sedimentary rocks
• Other metamorphic rocks
Metamorphic rocks
Metamorphism
• Takes place where preexisting rock is
subjected to temperatures and pressures
unlike those in which it formed
• Degrees of metamorphism
• Exhibited by rock texture and mineralogy
• Low-grade (e.g., shale becomes slate)
• High-grade (obliteration of original features)
Origin of pressure in
metamorphism
Figure 3.20
Metamorphic rocks
Metamorphic textures
• Foliated texture
• Minerals are in a parallel alignment
• Minerals are perpendicular to the
compressional force
• Nonfoliated texture
• Contain equidimensional crystals
• Resembles a coarse-grained igneous rock
Development of foliation due
to directed pressure
Figure 3.22
Classification of
metamorphic rocks
Figure 3.23
Metamorphic rocks
Common metamorphic rocks
• Foliated rocks
• Gneiss
• Strong segregation of silicate minerals
• "Banded" texture
• Nonfoliated rocks
• Marble
• Parent rock is limestone
• Large, interlocking calcite crystals
Gneiss typically displays
a banded appearance
Figure 3.24
Marble – a nonfoliated
metamorphic rock
Figure 3.24
3.5
Heat, pressure and fluids are active agents in
metamorphism. These processes change rocks by
1. increasing crystal size.
2. reorienting mineral grains.
3. forming new minerals.
4. increasing density.
5. All of the above.
3.5
Heat, pressure and fluids are active agents in
metamorphism. These processes change rocks by
1. increasing crystal size.
2. reorienting mineral grains.
3. forming new minerals.
4. increasing density.
5. All of the above.
Note: The granite rock on the left
(igneous) under pressure has had
its minerals become recrystallized
and reoriented with metamorphism.
The metamorphosed rock is a
gneiss.
Resources from rocks
and minerals
Metallic mineral resources
• Gold, silver, copper, mercury, lead, etc.
• Concentrations of desirable materials are
produced by
• Igneous processes
• Metamorphic processes
Resources from rocks
and minerals
Nonmetallic mineral resources
• Make use of the material’s
• Nonmetallic elements
• Physical or chemical properties
• Two broad groups
• Building materials (e.g., limestone, gypsum)
• Industrial minerals (e.g., fluorite, corundum,
sylvite)
Minerals used per person per year in the USA
Summary
• Minerals are made of atoms
– half silicates (in continental crust)
– half others
• Rocks are made of minerals
– Igneous
– Sedimentary
– Metamorphic
• We mine tremendous quantities each
year
75